在Swift iOS中无法使用dispatch_async方法更新UILabel

Question

I am setting json string value to UILabel using dispatch_async method. But Its unable to show updated value , but when I am printing label text, its showing updated value. here is my code-

 override func viewDidLoad() {
     super.viewDidLoad()
     get_detail_postmethod(url, params: params)
}

 func get_detail_postmethod(url: String, params: String) {
    let request = NSMutableURLRequest(URL: NSURL(string: url)!)
    request.HTTPMethod = "POST"
    let postString = params
    print("param=\(params)")
    request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
        guard error == nil && data != nil else {                                                          // check for fundamental networking error
            print("error=\(error)")
            return
        }

        if let httpStatus = response as? NSHTTPURLResponse where httpStatus.statusCode != 200 {           // check for http errors
            print("statusCode should be 200, but is \(httpStatus.statusCode)")
            print("response = \(response)")

        }

        let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
        print("responseString = \(responseString)")
        do{
            let json = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments)
            print(json)
           if let success = json["success"] as? Int
            {
            if((success) == 1){

             self.extract_json(data!)

            }
            else{

            }
            }

        }catch {
            print("Error with Json: \(error)")
        }
    }
    task.resume()
}

and below code for extract json data and set String value to UILabel-

func extract_json(jsonData:NSData)
{
    let json: AnyObject?
    do {
        json = try NSJSONSerialization.JSONObjectWithData(jsonData, options: [])
        print("full data \(json!)")
    } catch {
        json = nil
        return
    }
    let user_object = json!["opportunity_master"] as! NSArray
    let data_block = user_object[0] as? NSDictionary
    self.opp_title = (data_block!["opportunity_title"] as? String)!
    self.event_sdate = (data_block!["event_start_date"] as? String)!

    dispatch_async(dispatch_get_main_queue(), {
        print(self.opp_title)
        self.Event_title.text? = self.opp_title
        self.Txt_event_date.text = self.event_sdate
        self.Event_title.setNeedsDisplay()

        print("event title label \(self.Event_title.text)")

    })

}

I am not able to update values. Please suggest is there any other way to implement update UiLabel text.

Answer 1

This is solved by calling Viewcontroller like this-

let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let Opprt_Controller = storyboard.instantiateViewControllerWithIdentifier("Opprtunity_Event") as! Opportunity_Event

    self.navigationController!.pushViewController(Opprt_Controller, animated: true)

Answer 2

Try the below code to update your Label :

NSOperationQueue.mainQueue().addOperationWithBlock({ () -> Void in
        print(self.opp_title)
        self.Event_title.text? = self.opp_title
        self.Txt_event_date.text = self.event_sdate
        self.Event_title.setNeedsDisplay()
        print("event title label \(self.Event_title.text)") 

})

Answer 3

在viewDidAppear中而不是viewDidLoad中调用get_detail_postmethod（url，params：params）方法。

Answer 4

There is a syntax error in your dispatch_async method. Update code block with following.

dispatch_async(dispatch_get_main_queue()) {
    print(self.opp_title)
    self.Event_title.text? = self.opp_title
    self.Txt_event_date.text = self.event_sdate
    self.Event_title.setNeedsDisplay()

    print("event title label \(self.Event_title.text)")
}